This application claims priority from German Application No. 199 56 686.0, filed on Nov. 25, 1999, the subject matter of which is hereby incorporated herein by reference.
1. Field of the Invention
The present invention provides nucleotide sequences of coryneform bacteria coding for the genes sucC and sucD and a process for the fermentative production of amino acids, in particular L-lysine and L-glutamate, using bacteria in which the sucC- and/or sucD-gene is/are attenuated.
2. Background Information
L-amino acids, in particular L-lysine and L-glutamate, are used in human medicine and in the pharmaceutical industry, in the foodstuffs industry, and most particularly in animal nutrition.
It is known that amino acids can be produced by fermentation of strains of coryneform bacteria, in particular Corynebacterium glutamicum (C. glutamicum). On account of the great importance of amino acids efforts are constantly being made to improve production processes. Improvements in production may involve fermentation technology measures, such as, for example, stirring and provision of oxygen, or altering the composition of the nutrient media, such as for example the sugar concentration during fermentation or the working-up to the product form by, for example, ion exchange chromatography, or improving the intrinsic output properties of the microorganism itself.
Methods involving mutagenesis, selection and choice of mutants are used to improve the output properties. In this way strains are obtained that are resistant to antimetabolites or are auxotrophic for regulatory important metabolites, and that produce amino acids.
For some years recombinant DNA technology methods have also been used to improve Corynebacterium strains producing L-amino acids.
It is an object of the invention to provide new means for improving the fermentative production of amino acids, in particular L-lysine and L-glutamate.
Where L-amino acids or amino acids are mentioned hereinafter, it is to be understood that these terms refer to one or more amino acids, including their salts, selected from the group comprising L-asparagine, L-threonine, L-serine, L-glutamate, L-glycine, L-alanine, L-cysteine, L-valine, L-methionine, L-isoleucine, L-leucine, L-tyrosine, L-phenylalanine, L-histidine, L-lysine, L-tryptophan and L-arginine. L-lysine and L-glutamate are particularly preferred.
The present invention provides an isolated polynucleotide containing a polynucleotide sequence selected from the group comprising
a) a polynucleotide that is at least 70% identical to a polynucleotide encoding a polypeptide, that contains the amino acid sequence of SEQ ID NO:2,
b) a polynucleotide that is at least 70% identical to a polynucleotide encoding a polypeptide, that contains the amino acid sequence of SEQ ID NO:3,
c) a polynucleotide encoding a polypeptide, that contains an amino acid sequence that is at least 70% identical to the amino acid sequence of SEQ ID NO:2,
d) a polynucleotide encoding a polypeptide, that contains an amino acid sequence that is at least 70% identical to the amino acid sequence of SEQ ID NO:3,
e) a polynucleotide that is complementary to the polynucleotides of a), b), c) or d), and
f) a polynucleotide containing at least 15 successive nucleotides of the polynucleotide sequence of a), b), c), d) or e),
the polypeptide preferably exhibiting the activity of succinyl-CoA synthetase.
The present invention also provides the polynucleotide with the aforementioned features, which is preferably a replicable DNA containing:
(i) the nucleotide sequence shown in SEQ ID NO:l, or
(ii) at least one sequence that corresponds to the sequence (i) within the region of degeneration of the genetic code, or
(iii) at least one sequence that hybridizes with the sequence complementary to the sequence (i) or (ii), and optionally
(iv) functionally neutral sense mutations in (i).
The invention furthermore provides:
a polynucleotide as described above, containing the nucleotide sequence as shown in SEQ ID NO:1,
a polynucleotide according to claim 1, wherein the polynucleotide is a preferably recombinant DNA replicable in coryneform bacteria,
a vector containing parts of the polynucleotide according to the invention, but at least 15 successive nucleotides of the claimed sequence,
and coryneform bacteria in which the sucC- and/or sucD-gene is/are attenuated in particular by an insertion or deletion.
The present invention moreover provides polynucleotides that substantially comprise a polynucleotide sequence, that can be obtained by screening a corresponding gene library by means of hybridization, that contains the complete sucC- and/or sucD-gene with the polynucleotide sequence corresponding to SEQ ID NO:1 with a probe that contains the sequence of the aforementioned polynucleotide according to SEQ ID NO:1 or a fragment thereof, and isolation of the aforementioned DNA sequence.
Polynucleotides that contain the sequences according to the invention are suitable as hybridization probes for RNA, cDNA and DNA, in order to isolate cDNA, nucleic acids and/or polynucleotides or genes in their full length that code for succinyl-CoA synthetase, and to isolate such cDNA or genes whose sequence has a high similarity to that of the succinyl-CoA synthetase genes.
Polynucleotides that contain the sequences according to the invention are furthermore suitable as primers, by means of which DNA can be produced by the polymerase chain reaction (PCR) from genes that code for succinyl-CoA synthetase. Such oligonucleotides serving as probes or primers contain at least 30, preferably at least 20, and most particularly preferably at least 15 successive nucleotides. Nucleotides with a length of at least 40 or 50 nucleotides are also suitable.
xe2x80x9cIsolatedxe2x80x9d means separated from its natural environment.
xe2x80x9cPolynucleotidexe2x80x9d refers in general to polyribonucleotides and polydeoxyribonucleotides, in which connection these terms may refer to unmodified RNA or DNA or modified RNA or DNA.
By the term xe2x80x9cpolypeptidesxe2x80x9d are understood peptides or proteins that contain two or more amino acids bound via peptide bonds.
The polypeptides according to the invention include the polypeptides according to SEQ ID NO:2 and SEQ ID NO:3, in particular those having the biological activity of succinyl-CoA synthetase as well as those that are at least 70% identical to the polypeptide according to SEQ ID NO:2 or SEQ ID NO:3, and preferably at least 80% and particularly preferably at least 90% to 95% identical to the polypeptide according to SEQ ID NO:2 or SEQ ID NO:3 and that have the aforementioned activity.
The present invention furthermore relates to a process for the fermentative production of amino acids selected from the group comprising L-asparagine, L-threonine, L-serine, L-glutamate, L-glycine, L-alanine, L-cysteine, L-valine, L-methionine, L-isoleucine, L-leucine, L-tyrosine, L-phenylalanine, L-histidine, L-lysine, L-tryptophan and L-arginine, in particular L-lysine and L-glutamate, using coryneform bacteria that in particular already produce the amino acids, especially L-lysine and/or L-glutamate, and in which the nucleotide sequences coding for the sucC- and/or sucD-gene are attenuated, and in particular are expressed at a low level.
The term xe2x80x9cattenuationxe2x80x9d describes in this connection the reduction or switching off of the intracellular activity of one or more enzymes (proteins) in a microorganism that can be encoded by the corresponding DNA, by for example using a weak promoter or a gene and/or allele that encodes a corresponding enzyme with a low activity and/or inactivates the corresponding gene or enzyme (protein) and optionally combines these features.
The microorganisms that are the subject of the present invention can produce amino acids, in particular L-lysine, from glucose, sucrose, lactose, fructose, maltose, molasses, starch, cellulose or from glycerol and ethanol. The microorganisms may be types of coryneform bacteria, in particular of the genus Corynebacterium. In the genus Corynebacterium there should in particular be mentioned the type Corynebacterium glutamicum, which is known to those skilled in the art for its ability to produce L-amino acids.
Suitable strains of the genus Corynebacterium, in particular of the type Corynebacterium glutamicum, are in particular the following known wild type strains
Corynebacterium glutamicum ATCC13032
Corynebacterium acetoglutamicum ATCC15806
Corynebacterium acetoacidophilum ATCC13870
Corynebacterium melassecola ATCC17965
Corynebacterium thermoaminogenes FERM BP-1539
Brevibacterium flavum ATCC14067
Brevibacterium lactofermentum ATCC13869 and
Brevibacterium divaricatum ATCC14020
and mutants and/or strains obtained therefrom that produce L-amino acids, such as for example the L-lysine-producing strains.
Corynebacterium glutamicum FERM-P 1709
Brevibacterium flavum FERM-P 1708
Brevibacterium lactofermentum FERM-P 1712
Corynebacterium glutamicum FERM-P 6463
Corynebacterium glutamicum FERM-P 6464 and
Corynebacterium glutamicum DSM 5714.
The new genes sucC and sucD coding for the enzyme succinyl-CoA synthetase (EC 6.2.1.5) have been isolated from C. glutamicum. 
In order to isolate the sucC- and/or the sucD-gene or also other genes from C. glutamicum, a gene library of this microorganism is first of all constructed in E. coli. The construction of gene libraries is described in generally known textbooks and handbooks. By way of example there may be mentioned the textbook by Winnacker: Gene und Klone, Eine Einfuhrung in die Gentechnologie (Genes and Clones, An Introduction to Gene Technology) (Verlag Chemie, Weinheim, Germany, 1990) or the handbook by Sambrook et al.: Molecular Cloning, A Laboratory Manual (Cold Spring Harbor Laboratory Press, 1989). A very well-known gene library is that of the E. coli K-12 strain W3110, which has been cultivated by Kohara et al. (Cell 50, 495-508 (1987)) in xcex-vectors. Bathe et al. (Molecular and General Genetics, 252:255-265, 1996) describe a gene library from C. glutamicum ATCC13032 that has been prepared with the aid of the cosmid vector SuperCos I (Wahl et al., 1987, Proceedings of the National Academy of Sciences USA, 84:2160-2164) in the E. coli K-12 strain NM554 (Raleigh et al., 1988, Nucleic Acids Research 16:1563-1575).
Bxc3x6rmann et al. (Molecular Microbiology 6(3), 317-326 (1992)) in turn describe a gene library obtained from C. glutamicum ATCC13032 using the cosmid pHC79 (Hohn and Collins, Gene 11, 291-298 (1980)). O""Donohue (The Cloning and Molecular Analysis of Four Common Aromatic Amino Acid Biosynthetic Genes from Corynebacterium glutamicum. Ph.D. Thesis, National University of Ireland, Galway, 1997) describes the cloning of C. glutamicum genes using the xcex Zap Expression system described by Short et al. (Nucleic Acids Research, 16: 7583).
In order to produce a gene library from C. glutamicum in E. coli, plasmids such as pBR322 (Bolivar, Life Sciences, 25, 807-818 (1979)) or pUC9 (Vieira et al., 1982, Gene, 19:259-268) may also be used. Particularly suitable as hosts are those E. coli strains that are restriction-defective and recombinant-defective, such as for example the strain DH5xcex1 (Jeffrey H. Miller: xe2x80x9cA Short Course in Bacterial Genetics, A Laboratory Manual and Handbook for Escherichia coli and Related Bacteriaxe2x80x9d, Cold Spring Harbour Laboratory Press, 1992).
The long DNA fragments cloned with the aid of cosmids or other xcex-vectors may then in turn be sub-cloned into accessible vectors suitable for DNA sequencing.
Methods for DNA sequencing are described inter alia by Sanger et al. (Proceedings of the National Academy of Sciences of the United States of America, 74:5463-5467, 1977).
The DNA sequences that are obtained may then be investigated with known algorithms and/or sequence analysis programs, such as for example that of Staden (Nucleic Acids Research 14, 217-232(1986)), the GCG-programme of Butler (Methods of Biochemical Analysis 39, 74-97 (1998)), the FASTA algorithm of Pearson and Lipman (Proceedings of the National Academy of Sciences USA 85,2444-2448 (1988)) or the BLAST algorithm of Altschul et al. (Nature Genetics 6, 119-129 (1994)) and compared with the sequence entries listed in publicly accessible data banks. Publicly accessible data banks for nucleotide sequences are for example those of the European Molecular Biologies Laboratories (EMBL, Heidelberg, Germany) or those of the National Center for Biotechnology Information (NCBI, Bethesda, Md., USA).
The new DNA sequences of C. glutamicum encoding the sucC- and sucD-genes have been discovered, and as SEQ ID No. 1 are part of the present invention. The amino acid sequence of the corresponding proteins has furthermore been derived from the existing DNA sequences using the methods described above. The resultant amino acid sequences of the sucC- and sucD-gene product are shown in SEQ ID NO:2 and SEQ ID NO:3.
Coding DNA sequences that arise from SEQ ID NO:1 due to the degeneracy of the genetic code are also included in the invention. In the same way DNA sequences that hybridize with SEQ ID No. 1 or parts of SEQ ID No. 1 are the subject of the invention. Finally, DNA sequences that are produced by the polymerase chain reaction (PCR) using primers obtained from SEQ ID No. 1 are also the subject of the invention.
The person skilled in the art will find information on identifying DNA sequences by means of hybridization in, inter alia, the handbook xe2x80x9cThe DIG System User""s Guide for Filter Hybridizationxe2x80x9d published by Boehringer Mannheim GmbH (Mannheim, Germany, 1993) and in Liebl et al. (International Journal of Systematic Bacteriology (1991) 41: 255-260). The hybridization takes place under stringent conditions, in other words only hybrids are formed in which the probe and target sequence, i.e. the polynucleotides treated with the probe, are at least 70% identical. It is known that the thoroughness of the hybridization including the washing stages is influenced or even determined by varying the buffer composition, temperature and the salt concentration. The hybridization reaction is preferably carried out at a relatively low degree of thoroughness compared to the washing stages (Hybaid Hybridisation Guide, Hybaid Limited, Teddington, UK, 1996).
A 5xc3x97SSC-buffer for example may be used at a temperature of ca. 50-68xc2x0 C. for the Hybridization reaction. In this connection probes may also be hybridized with polynucleotides that have less than 70% identity with the sequence of the probe. Such hybrids are less stable and are removed by washing under stringent conditions. This may be effected for example by reducing the salt concentration to 2xc3x97SSC and optionally subsequently to 0.5xc3x97SSC (The DIG System User""s Guide for Filter Hybridization, Boehringer Mannheim, Mannheim, Germany, 1995), a temperature of ca. 50-68xc2x0 C. being maintained. It is also optionally possible to reduce the salt concentration down to 0.1xc3x97SSC. By stepwise raising of the Hybridization temperature in steps of ca. 1-2xc2x0 C. from 50 to 68xc2x0 C., polynucleotide fragments can be separated that exhibit for example at least 70% or at least 80% or at least 90% to 95% identity to the sequence of the probe that is used. Further instructions for hybridization are available on the market in the form of so-called kits (e.g. DIG Easy Hyb von der Firma Roche Diagnostics GmbH, Mannheim, Germany, Catalog No. 1603558).
The person skilled in the art can find details of the enhancement of DNA sequences by means of the polymerase chain reaction (PCR) in, inter alia, the handbook by Gait: Oligonucleotide synthesis: A Practical Approach (IRL Press, Oxford, UK, 1984) and in Newton and Graham: PCR (Spektrum Akademischer Verlag, Heidelberg, Germany, 1994).
It has now been found that coryneform bacteria produce L-amino acids, in particular L-lysine, in an improved manner after attenuation of the sucC- and/or sucD-gene.
In order to achieve such an attenuation, either the expression of the sucC- and/or sucD-gene or the catalytic properties of the enzyme proteins can be reduced or switched off. Both measures may optionally be combined.
The reduction of the gene expression may be achieved by suitable culture conditions or by genetic alteration (mutation) of the signal structures of the gene expression. Signal structures of the gene expression are for example repressal genes, activator genes, operators, promoters, attenuators, ribosome bonding sites, the start codon and terminators. The person skilled in the art can find information on the above in for example patent application WO 96/15246, in Boyd and Murphy (Journal of Bacteriology 170: 5949 (1988)), in Voskuil and Chambliss (Nucleic Acids Research 26: 3548 (1998), in Jensen and Hammer (Biotechnology and Bioengineering.58: 191 (1998)), in Patek et al. (Microbiology 142: 1297 (1996)) and in known textbooks on genetics and molecular biology, such as for example the textbook by Knippers (xe2x80x9cMolekulare Genetikxe2x80x9d, 6th Edition, Georg Thieme Verlag, Stuttgart, Germany, 1995) or the textbook by Winnacker (xe2x80x9cGene und Klonexe2x80x9d, VCH Verlagsgesellschaft, Weinheim, Germany, 1990).
Mutations that lead to an alteration and/or reduction of the catalytic properties of enzyme proteins are known in the prior art; there may be mentioned by way of example the work carried out by Qiu and Goodman (Journal of Biological Chemistry 272: 8611-8617 (1997)), Sugimoto et al. (Bioscience Biotechnology and Biochemistry 61: 1760-1762 (1997)) and Mxc3x6ckel (xe2x80x9cDie Threonindehydratase aus Corynebacterium glutamicum: Aufhebung der allosterischen Regulation und Struktur des Enzymsxe2x80x9d, (xe2x80x9cThe Threonine Dehydratase from Corynebacterium glutamicum: Cancellation of the Allosteric Regulation and Structure of the Enzymexe2x80x9d), reports of the Jxc3xclichs Research Centre, Jxc3xcl-2906, ISSN09442952, Jxc3xclich, Germany, 1994). Overviews and summaries may be obtained from known textbooks on genetics and molecular biology, such as for example those by Hagemann (xe2x80x9cAllgemeine Genetikxe2x80x9d (xe2x80x9cGeneral Geneticsxe2x80x9d), Gustav Fischer Verlag, Stuttgart, 1986).
Mutations cover such phenomena as transitions, transversions, insertions and deletions. Depending on the effect of the amino acid exchange on the enzyme activity, one speaks of missense mutations or nonsense mutations.
Insertions or deletions of at least one base pair in a gene lead to frame shift mutations, as a result of which false amino acids are incorporated or the translation is prematurely arrested. Deletions of several codons typically lead to a complete suppression of the enzyme activity. Details of producing such mutations are part of the prior art and can be obtained from known textbooks on genetics and molecular biology, such as for example the textbook by Knippers (xe2x80x9cMolekulare Genetikxe2x80x9d, 6th Edition, Georg Thieme Verlag, Stuttgart, Germany, 1995), that by Winnacker (xe2x80x9cGene und Klonexe2x80x9d, VCH Verlagsgesellschaft, Weinheim, Germany, 1990) or that by Hagemann (xe2x80x9cAllgemeine Genetikxe2x80x9d, Gustav Fischer Verlag, Stuttgart, 1986).
A conventional method of mutating genes of C. glutamicum is the method of gene disruption and gene replacement described by Schwarzer and Puhler (Bio/Technology 9, 84-87 (1991)).
In the method of gene disruption a central part of the coding region of the gene that is of interest is cloned in a plasmid vector that can replicate in a host (typically E. coli), but not in C. glutamicum. Vectors that may be used include for example pSUP301 (Simon et al., Bio/Technology 1, 784-791 (1983)), pK18mob or pK19mob (Schxc3xa4fer et al., Gene 145, 69-73 (1994)), pK18mobsacB or pK19mobsacB (Jxc3xa4ger et al., Journal of Bacteriology 174: 5462-65 (1992)), pGEM-T (Promega Corporation, Madison, Wis., USA), pCR2.1-TOPO (Shuman (1994). Journal of Biological Chemistry 269:32678-84; U.S. Pat. No. 5,487,993), pCR(copyright)Blunt (Firma Invitrogen, Groningen, Niederlande; Bernard et al., Journal of Molecular Biology, 234: 534-541 (1993)) or pEM1 (Schrumpf et al, 1991, Journal of Bacteriology 173:4510-4516). The plasmid vector that contains the central part of the coding region of the gene is then converted by conjugation or transformation into the desired strain of C. glutamicum. 
The method of conjugation is described for example in Schxc3xa4fer et al. (Applied and Environmental Microbiology 60, 756-759 (1994)). Methods for transformation are described for example in Thierbach et al. (Applied Microbiology and Biotechnology 29, 356-362 (1988)), Dunican and Shivnan (Bio/Technology 7, 1067-1070 (1989)) and Tauch et al. (FEMS Microbiological Letters 123, 343-347 (1994)). After homologous recombination by means of a crossover event, the coding region of the affected gene is disrupted by the vector sequence and two incomplete alleles are obtained, each of which lacks the 3xe2x80x2- and the 5xe2x80x2-end. This method has been used for example by Fitzpatrick et al. (Applied Microbiology and Biotechnology 42, 575-580 (1994)) in order to switch off the recA-gene of C. glutamicum. The sucC- and/or sucD-gene may be switched off in this way.
In the method of gene replacement a mutation, such as for example a deletion, insertion or base exchange is produced in vitro in the gene that is of interest. The allele that is produced is in turn cloned in a vector that is not replicative for C. glutamicum and the vector is then converted by transformation or conjugation into the desired host for C. glutamicum. The incorporation of the mutation and/or of the allele in the target gene and/or in the target sequence is achieved after homologous recombination by means of a first crossover event effecting integration and an appropriate second crossover event effecting excision. This method has been used for example by Peters-Wendisch (Microbiology 144, 915-927 (1998)) in order to switch off the pyc-gene of C. glutamicum by means of a deletion. A deletion, insertion or a base exchange can be incorporated into the sucC- and/or sucD-gene in this way.
A deletion, insertion or a base exchange can be incorporated into the sucC- and/or sucD-gene in this way.
Furthermore it may be advantageous for the production of L-amino acids, in particular L-lysine, in addition to enhance, in particular to over-express, one or more enzymes of the relevant biosynthesis pathway, glycolysis, anaplerotic, citric acid cycle or amino acid export, in order to attenuate the sucC- and/or sucD-gene.
Thus, in the production of L-lysine and/or L-glutamate, in addition to the attenuation of the sucC- and/or sucD-gene, one or more of the genes selected from the following group may be enhanced, in particular over-expressed:
the dapA-gene encoding dihydrodipicolinate-synthase (EP-B 0 197 335),
the gap-gene encoding glyceraldehyde-3-phosphate dehydrogenase (Eikmanns (1992), Journal of Bacteriology 174:6076-6086),
the gene tpi encoding triosephosphate isomerase (Eikmanns (1992), Journal of Bacteriology 174:6076-6086),
the gene pgk encoding 3-phosphoglycerate kinase (Eikmanns (1992), Journal of Bacteriology: 174:6076-6086),
the pyc-gene encoding pyruvate carboxylase (Eikmanns (1992), Journal of Bacteriology 174:6076-6086),
the mqo-gene encoding malate:quinone oxidoreductase (Molenaar et al., European Journal of Biochemistry 254, 395-403 (1998)),
the gene lysC encoding a feed-back resistant aspartate kinase (Accession No.P26512),
the lysE-gene encoding the L-lysine-export (DE-A-195 48 222),
the gene zwa1 encoding the Zwa1-protein (DE: 19959328.0, DSM 13115).
Moreover, it may be advantageous for the production of L-lysine and/or L-glutamate, in addition to the attenuation of the sucC- and/or sucD-gene, at the same time to attenuate, in particular to reduce the expression of one or more of the genes selected from the group comprising:
the gene pck encoding phosphoenolpyruvate-carboxykinase (DE 199 50 409.1, DSM 13047),
the gene pgi encoding glucose-6-phosphate isomerase (U.S. Ser. No. 09/396,478, DSM 12969),
the gene poxB encoding pyruvate-oxidase (DE:1995 1975.7, DSM 13114),
the gene zwa2 encoding the zwa2-protein (DE: 19959327.2, DSM 13113).
In addition it may be advantageous for the production of amino acid, in particular L-lysine and/or L-glutamate, in addition to the attenuation of the sucC- and/or sucD-gene to switch off undesirable secondary reactions (Nakayama: xe2x80x9cBreeding of Amino Acid Producing Microorganismsxe2x80x9d, in: Overproduction of Microbial Products, Krumphanzl, Sikyta, Vanek (eds.), Academic Press, London, UK, 1982).
The microorganisms containing the polynucleotide of aforementioned features a)-f) are also the subject of the invention and may be cultured continuously or batchwise in a batch process (batch cultivation) or in a fed batch or repeated fed batch process in order to produce L-amino acids, in particular L-lysine. An overview of known cultivation methods is given in the textbook by Chmiel (Bioprozesstechnik 1. Einfxc3xchrung in die Bioverfahrenstechnik (Biological Process Technology, Introduction to Biological Engineering)(Gustav Fischer Verlag, Stuttgart, 1991)) or in the textbook by Storhas (Bioreaktoren und periphere Einrichtungen (Bioreactors and Peripheral Equipment)(Vieweg Verlag, Braunschweig/Wiesbaden, 1994)).
The culture medium to be used must suitably satisfy the demands of the relevant strains. Descriptions of culture media for various microorganisms are given in the handbook xe2x80x9cManual of Methods for General Bacteriologyxe2x80x9d of the American Society for Bacteriology (Washington D.C., USA, 1981).
As carbon source there may be used sugars and carbohydrates such as for example glucose, sucrose, lactose, fructose, maltose, molasses, starch and cellulose, oils and fats such as for example soya bean oil, sunflower oil, groundnut oil and coconut oil, fatty acids such as for example palmitic acid, stearic acid and linoleic acid, alcohols such as for example glycerol and ethanol, and organic acids such as for example acetic acid. These substances may be used individually or as a mixture.
As nitrogen source there may be used organic nitrogen-containing compounds such as peptones, yeast extract, meat extract, malt extract, corn steep liquor, soya bean flour and urea, or inorganic compounds such as ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium carbonate and ammonium nitrate. The nitrogen sources may be used individually or as a mixture.
As phosphorus source there may be used phosphoric acid, potassium dihydrogen phosphate or dipotassium hydrogen phosphate, or the corresponding sodium-containing salts. The culture medium must furthermore contain salts of metals such as for Example magnesium sulfate or iron sulfate that are necessary for growth. Finally, essential growth substances such as amino acids and vitamins may, in addition to the substances mentioned above, be used. Apart from this, suitable precursors may be added to the culture medium. The aforementioned feedstock substances may be added to the culture in the form of a one-off addition, or may be metered in during the actual cultivation in a suitable way.
Alkaline compounds such as sodium hydroxide, potassium hydroxide, ammonia or ammonia water or acidic compounds such as phosphoric acid or sulfuric acid may be used in an appropriate manner in order to regulate the pH of the culture. Antifoaming agents such as for example fatty acid polyglycol esters may be used to prevent foam formation. Suitable selectively acting substances such as for example antibiotics may be added to the medium in order to maintain the stability of plasmids. Oxygen or oxygen-containing gas mixtures such as for example air are introduced into the culture in order to maintain aerobic conditions. The temperature of the culture is normally 20xc2x0 C. to 45xc2x0 C. and preferably 25xc2x0 C. to 40xc2x0 C. The culture is continued until a maximum yield of the desired product has been formed. This target is normally-achieved within 10 hours to 160 hours.
Methods for determining L-amino acids are known from the prior art. The analysis may be carried out as described for example by Spackman et al. (Analytical Chemistry, 30, (1958), 1190) by anion exchange chromatography followed by ninhydrin derivation or may be carried out by reverse phase HPLC, as described by Lindroth et al. (Analytical Chemistry (1979) 51: 1167-1174).